The present invention generally relates to an audio diaphragm for a radio telephone handset, and more particularly is concerned with how such an audio diaphragm can be mounted in a radio telephone handset.
Inside an average radio telephone handset there can usually be found several audio transducers incorporating audio diaphragms. Typically, the handset has a microphone, an ear piece/speaker transducer and a ringer. In a microphone the diaphragm is modulated by sound, whilst in a speaker transducer the diaphragm is sound modulating. Optionally the handset may be provided with additional audio transducers for facilitating other audio functions such as hands-free telephoning.
To date, in known radio telephone handsets, audio diaphragms are mounted in one of a number different ways. Common methods of mounting the diaphragm include attaching it directly to the front or back cover of the handset or supporting it on an internal assembly plate carrying other components of the handset. To give one example, in one known type of handset, a speaker diaphragm is attached to an internal chassis which is bounded by a printed circuit board.
Although existing mounting techniques are perfunctory in holding an audio diaphragm in place, all three basic arrangements outlined above share a number of common problems. One of the main problems is that of sound attenuation. Taking, for the purpose of explanation, a handset speaker diaphragm, for example for hands-free usage. As is known, a speaker diaphragm, in response to an electrical signal, produces sound waves which propagate simultaneously in forward and rearward directions substantially in opposite phases. Owing for example to internal reflections of the sound waves occurring in the handset, sound waves having opposing phases are caused to meet one another leading to some destructive interference taking place between the forward sound waves and the rearward sound waves, thus resulting in sound cancellation. The overall effect is a reduction in the output sound pressure level, as well as frequency response change. Given the restricted surroundings of a radio telephone handset, and the comparatively low operating frequency of handset speaker diaphragms, the problems of sound cancellation are particularly marked.
Staying with the example of handset speaker diaphragms, a further problem is that, with different designs of handsets having different structures, the frequency response and performance characteristics of a speaker are not found to be uniform across a range of handsets. This can be attributed in particular to internal dimensions which allow standing waves to occur causing dips in the acoustic response of the handset speaker. Consequently, the variation in the performance of the speaker is an added factor which must be taken into consideration at the design stage; otherwise there is a risk of sub-optimal speaker performance.
In addition to a deterioration in the actual sound quality of a handset speaker diaphragm, these acoustic losses inevitably lead the handset speaker to draw more power from the radio telephone battery in order to meet a given sound output requirement. In radio telephone handsets, where power efficiency is the key to battery life--and hence usefulness of the telephone--the cumulative effect of the problems of existing mounting techniques can be acute. Also, the handset speaker may cause more audible distortion as a result of the increased power.
Against this background, the present invention seeks to address the shortcomings of known arrangements for mounting an audio diaphragm/transducer in a radio telephone handset.